1. Field of the Invention
The present invention relates in general to a wireless media access method, more particularly, to a wireless media access method for preventing retransmission due to a high collision rate on a PAN (Personal Area Network) where node integration is high.
2. Description of the Related Art
A PAN (Personal Area Network), unlike a LAN or WAN, is a personal network owned by a personal individual. In other words, various devices are interconnected to construct a network exclusively for a personal use. The implementation of the PAN is a WPAN (Wireless Personal Area Network).
Currently, the IEEE 802.15.3 TG (Task Group) is developing a new standard for the WPAN technology. The IEEE 802.15.3 specifies raw data rates of 11 to 55 Mbps at distances within 10 meters without consuming much power. The IEEE 802.15.3a TG is now trying to develop a higher-rate physical layer, 100 Mbps for example, for the IEEE 802.15.3. Particularly, the IEEE 802.15.3a can be applied to wireless transmission of multimedia (e.g., moving images) within a short distance. Meanwhile, the IEEE 802.15.4 TG is aimed at developing standards for inexpensive, low-powered communication, which can be mainly applied to monitoring and control systems.
The basic unit of the WPAN is a piconet constructed of at least one device (DEV) sharing a single network identifier with a piconet coordinator (PNC). The PNC forms a temporary piconet by transmitting a beacon, and provides a basic communication timing (i.e., network synchronization timing). More specifically, the PNC provides devices on a piconet with wireless communication services, such as QoS, synchronization, a power save mode and a media access control (MAC).
According to the IEEE 802.15.3 standard, a piconet is formed whenever needed, and a plurality of devices on the piconet share one media in a peer to peer fashion and communicate with each other based on a multihop wireless system.
As described above, a plurality of devices on the piconet communicate with each other through one media. Therefore, to avoid the occurrence of collision in communications between devices, it is required to control each device's access to a wireless media, and to allow the devices to communicate at proper timings.
The wireless media access over the PAN is largely divided into a collision-based system and a collision avoidance system. A typical example of the collision-based system is a CSMA-CA used for the IEEE 802.11. The merits of this system are that it is relatively simple and has a small overhead. However, if the node integration increases, the rate of occurrence of a collision is increased and as a result of this, the number of retransmission also increases.
A typical example of the collision avoidance system is a TDMA used in broadband wireless system like HiperLAN2. Although the TDMA is free of collision due to simultaneous accesses, its resources allocated to control traffic are not effectively used and could be wasted.
In particular, as the number of devices interconnected over the PAN increases, the wireless media access contention is increased. Thus, the problems of the collision-based or collision avoidance systems become worse, and the wireless media access is available to a few devices only. Also, the rate of the occurrence of a collision is increased because many devices attempt to access the media, and this results in the increase of the number of retransmission, only causing a vicious circle of more collisions and delay in transmission.